1. Field of the Invention
The present invention relates to a photo mask blank and a photo mask preferably used in fine patterning for semiconductor integrated circuits, color filters for CCDs (charge coupled devices) and LCDs (liquid crystal displays) and magnetic heads and so forth.
2. Description of the Related Art
Photolithography technique utilizing a photo mask is used in fine patterning for high-density semiconductor integrated circuits such as LSIs, VLSIs, etc., color filters for CCDs (charge coupled devices) and LCDs (liquid crystal displays), and magnetic heads and so forth.
As the aforementioned photo mask, using a photo mask blank wherein a light-shielding film generally comprising chrome (Cr) is formed on a transparent substrate such as silica glass and aluminosilicate glass by sputtering method, vacuum evaporation method, etc., a desired pattern is formed on this light-shielding film to obtain the photo mask.
In fabrication of such a photo mask, a resist pattern is formed through the processes of, in order, coating a photo resist or an electron beam resist onto a photo mask blank wherein a light-shielding film is formed on a substrate, selectively exposing a desired pattern, developing, rinsing and drying. Subsequently, wet etching using an etchant containing a mixed aqueous solution of cerium ammonium nitrate and perchloric acid or dry etching using a chlorine gas is performed by using the resist pattern as a mask, the unmasked portion of chrome film has been removed, and then the resist is removed. Thereby, a photo mask in which a desired pattern with the light-shielding portions and light-transmitting portions can be produced.
In the case of using such a photo mask in lithography, because the reflectance of a Cr type light-shielding film is high, light reflected by a silicon wafer, etc. that are exposed objects travels through a projection lens, is reflected by the photo mask, and returns to the silicon wafer. In order to prevent such multiple reflection, normally an anti-reflection film is formed on the light-shielding film.
As a photo mask blank and photo mask having such an anti-reflection film, a photo mask blank in which a CrO film is formed as the anti-reflection film on the surface side of a Cr light-shielding film formed on a transparent substrate, and another anti-reflection film is formed at the interface between the Cr light-shielding film and the transparent substrate has been proposed (see, for example, Japanese Examined Publication No. S62-37385). And, an anti-reflection film using CrON has been disclosed (see, for example, Japanese Patent Nos. 1565243 and 1489613).
Also, using Cr (see, for example, Japanese Patent No. 1565243), CrC (see, for example, Japanese Patent No. 1420095), etc. for a light-shielding film is known.
Further, a mask blank in which a half-tone film is formed to increase resolution and a Cr film is formed thereon has been put into practice.
The reflectance of the blank is required to be low at exposure wavelength in order to prevent the above-mentioned multiple reflection between the photo mask and the exposed object such as a semiconductor substrate. On the other hand, with the market demand in recent years for higher integration in semiconductor integrated circuit etc., reduction in the minimum feature size of photo mask patterns has rapidly progressed. Such miniaturization has been achieved in part by the use of shorter wavelength exposure light. However, with the shortening of exposure wavelengths such as 248 nm, 193 nm and 157 nm, the problem has arisen that reflectance cannot be sufficiently reduced by an anti-reflection film using a Cr type film.